For an early account of what the architecture of multi-user environments in VRML look like, see [Environments].

applications

An overview of logic programming languages for the Internet is given in Andrew Davison's [Logic]. Due to its late arrival on the Web scene, DLP is not mentioned in this overview. It was, however, mentioned in a previous overview of the same author [Survey], in the category of object-oriented extensions. For your information, the principal investigator organized a workshop at WWW6 in 1997 entitled Logic Programming for the Web, [Workshop].

There have been a number of attempts to improve on the scripting capabilities of VRML. One example of interest, from our perspective, is the extension proposed in [Script], which allows for logic programming in VRML script nodes. This approach affects the VRML files themselves, and hence the VRML97 standard. As a drawback, existing VRML content cannot be (re)used without modification. More importntly, however, such an approach does not allow for migrating to newer or other scenegraph-based formats such as X3D or Java3D.

In effect, Jinni (developed by Paul Tarau) was a source of inspiration for our first DLP+VRML prototype, [Jinni]. Nevertheless, our DLP language is semantically more suited to deal with the complexities of a more tight coupling of VRML and logic programming. In particular, multi-threaded objects in DLP allow for receiving events in an asynchronous manner, which is impossible to do in ordinary sequential Prolog. Distributed applications in Jinni are possible using a Linda-style shared tuple space. In our approach we rely on rendez-vous communication and server-side mediator objects. As the soccer prototype shows, it is rather easy to create a shared repository of state information using agent communication primitives in DLP.

The DIVE project at the Swedish Institute of Computer Science is an example of a complex heterogeneous system for developing multi-user virtual communities, [DIVE]. It is offers support for a variety of graphic formats, including VRML, and allows for scripting behaviors and interactions using Tcl. DIVE applications and activities include virtual battlefields, spatial models of interaction, virtual agents, real-world robot control and multi-modal interaction. DIVE is supported on a variety of platforms. The first DIVE version appeared in 1991. Our approach clearly builds on later developments, in particular Java, to achieve cross-platform portability. In contrast to the heterogeneous nature of the DIVE platform, we provide a unified language framework as a programmatic interface for the creation of 3D content and behavioral properties.

The Dutch Parlevink project, at the University of Twente, has developed a virtual theater, which demonstrates that agents may usefully be employed in (VRML-based) virtual environments, [Parlevink] The focus of the Parlevink project, however, is more on cognitive models and natural language processing. In contrast, our goal is to improve virtual environment technology itself, by providing a unified framework for developing agents and virtual environments.

Finally, we cannot conclude this brief overview of related work without mentioning Alice, a 3D interactive programming environment for virtual worlds, developed at Carnegie-Mellon University, [Alice]. One interesting feature of Alice is that it allows for programming generic behavioral properties in the object-oriented scripting language Python. Nevertheless, we believe that due to the knowledge-intensive nature of the programming tasks required for developing real applications in rich media virtual environments, a logic-based language such as DLP will in the long end be much more effective.

embedding in education: focus on multimedia

focus on multimedia